how browserSync makes livereload with a .test domain?

how makes browserSync works with domain? not localhost

by example if I run this:

mix.browserSync({
        proxy: "mysite.test"
    });

I got his:

[Browsersync] Proxying: http://mysite.test
[Browsersync] Access URLs:
 ---------------------------------------
       Local: http://localhost:3000
    External: http://192.168.100.16:3000
 ---------------------------------------
          UI: http://localhost:3001
 UI External: http://localhost:3001

on the browser: if I hit localhost and make code changes, yes, reload great! but I don't want use localhost, I want use the test domain, if I run mysite.test nothing happens, code changes but not reload.

so what's the big deal of Proxying: http://mysite.test , I mean yes I can see the site on mysite.test but Browsersync not make any livereload on that domain, only on localhost.